22 



BULLETIN 604, U. S. DEPARTMENT OP AGRICULTURE. 



eluding this tree from the higher mountains. To a limited extent, 

 heat may have some influence in fixing its lower limits. However, in 

 view of the continued high temperatures which the tree is known to 

 endure, it is doubtful whether heat has this effect, except as it reduces 

 an already meager supply of moisture by causing excessive evap- 

 oration. 



SOIL. 



Of all the various factors affecting the occurrence of incense cedar, 

 soil is probably the least important. The best proof of its adapta- 

 bility in this respect is the fact that throughout its range it is found 

 growing on soils of every description, bowlder wash and wet adobe 

 excepted. 



GROWTH. 



Incense cedar is naturally a slow-growing tree. Under favorable 

 conditions, however, its growth is fairly rapid, although it can not 

 compete successfully with its more aggressive associates, sugar pine, 

 yellow pine, and white fir. 



HEIGHT GROWTH. 



Table 12, which is based on stem analysis of 1,000 seedlings, shows 

 the extremely slow growth of this species during the seedling stage 

 under the average conditions prevailing in virgin stands. 



Table 12. — Incense cedar, seedling growth (age-height) ; basis, 1,000 seedlings. 



[curved.] 



Age. 



Height in feet. 



Age. 



Height in feet. 



Average 

 heights 



of all 



seedlings 



below the 



mean. 



Mean, 

 height. 



Average 

 heights 



of all 



seedlings 



above the 



mean. 



Average 

 heights 

 of all 

 seedlings 

 below the 

 mean. 



Mean, 

 height. 



Average 

 heights 



of all 



seedlings 



above the 



mean. 



Years. 



5 



10 



15 



20 



0.2 

 .5 

 .9 



1.3 



0.5 

 1.1 

 1.6 

 2.2 



1.0 



2.0 

 2.9 

 3.9 



Years. 

 25 

 30 

 35 



1.7 

 2.1 

 2.6 



2.7 

 3.3 

 3.9 



5.1 











Under ordinary conditions, suppression is doubtless responsible 

 to a large extent for this extremely slow growth, since reproduction, 

 as a rule, occurs only in small openings or under the half light of 

 a high forest, where the encouragement for rapid growth is small. 

 In the larger openings and on cut-over lands, where light is abund- 

 ant seedlings shoot up rapidly after they have once become thor- 

 oughly established. In fact, in all cases except those of extreme 



